Baffle for loud speakers



Patented June 18, 1935 UNITED STATES PATENT OFFICE 8 Claims.

My invention is a novel baflle for use in conjunction with electro-dynamic loud speakers, 2. term commonly designating a large number of different acoustical devices for translation or con version of electrical waves into sound waves, my

novel bafiie being especially designed for use with loud speakers in sound reproduction by radios, phonographs, public address systems, moving pictures, and all similar devices involving reproduction of sound by electrical means.

The principal objects are briefly to provide a foldable battle for loud speakers of sufiicient area to fully reproduce musical notes in the lower register, 1. e., of the order of thirty to sixty cycles; also to provide a ballle in the form of a screen hav ing a flat ornamental front surface, open at the rear, making possible the elimination of distortion due to the resonance such as is set up in a cabinet or other enclosure, and the rear face having' a high sound absorption coefficient effective in dissipating all sound waves reflected from walls or other surfaces against which the baffle might be placed.

A further object is to provide a bafile screen of practical value from a utilitarian as well as an ornamental standpoint, the same being constructed of materials which lend themselves to a variety of decorative schemes to harmonize with any surroundings.

Acoustical engineers have long sought a practlcal means for faithfully reproducing from loud speakers or the like music in the lower registers. To do this a baffle or partition mmt necessarily be used for separating the sound waves generated in front of a loud speaker from those waves generated in back thereof. Sound Waves generated in back of a loud speaker are of the same intensity as those generated in front but are in opposite phase, and therefore the waves set up on in back of a loud speaker tend to dampen the waves set up on at the front unless the air between the front and back is separated by a baffle. In the case of high notes, the cone itself usually forms a sufficient baflle, but for notes of the lower registers a larger baflle is required in order that the sound waves will be faithfully reproduced, i.- 'e., without dampening as above explained.

I have discovered that a baffle, to be effective, must be such that the shortest air path between the front and back sides of the loud speaker is at least onequarter of the wave length of the note reproduced; and that in order to properly reproduce a note two octaves below middle C (54 cycles) a bafiie about 51 inches square is required,

while proper reproduction of a note three octaves below middle C (32 cycles) requires a baffle about 102 inches square. I have also found that a baffle 60 inches square will faithfully reproduce the fundamental frequencies down to cycles and also reproduce the first harmonics of all musical frequencies below that, leaving nothing to be desired in the way of realism.

The need of a bafiie which would be acceptable in appearance gave rise to the use of cabinets of relatively large size for the installation of radios, but use of cabinets for this purpose has many drawbacks. The sound waves generated in back or" a loud speaker are of the same intensity as those in front, and this intensity in even a partial enclosure will create sound waves of considerable reverberation. In addition, any cabinet has its own frequency or vibration pitch somewhere in the lower audible range, and when notes of this frequency are struck, further unwanted sounds arise which add to the distortion. In attempting to overcome this difficulty many late cabinet models have been constructed without bottom panels, thereby reducing some reverberation but at the same time defeating the already very limited bafiie effect of the cabinet; and further reverberation is caused by the sound waves generated in back of the loud speaker being reflected back and forth between the smooth surfaces of the wall and cabinet.

My novel baflle for loud speakers obviates all the above mentioned objections to cabinet baffles; and my invention provides a baflle of the necessary area, both horizontally and vertically,

designed according to acoustic principles and ne- 3 cessities, and being effective in both horizontal and vertical directions, is most effective; also a baffle acceptable as an object of beauty, and useful as an article of furniture; and an article standard in design, which has found accepted usage as an item of decoration as Well as of utility.

' I will explain the invention with reference to the accompanying drawing which illustrates one practical embodiment thereof to enable others familiar with the art to adopt and use the same, and will summarize in the claims the novel features of construction, and novel combinations of parts, for which protection is desired.

In said drawing:

Fig. 1 is a front view of the baffle showing the ornamentation on the front of the panels partly removed.

Fig. 2 is a rear perspective View thereof, showing the stand carrying the loud speaker detachably secured to the middle panel.

Fig. 3 is an enlarged section on the line 3-3, Fig. 1.

Fig. 4 is a section on the line 4-4, Fig. 2, illustrating the method of detachably attaching the loud speaker stand to the middle section of the baffle.

In the practical utilization of my invention my baffle is embodied in the form of a decorative or ornamental folding screen, preferably a standard three-panel hinged screen in sections, but may comprise a screen containing one, two, three or more sections intended to be painted or deoorated and used as an item of furniture in the capacity of ornamentation or utility, the use of the side sections when a plurality of sections are used providing the required bafiie area without loss of portability.

My novel baffle as shown in the drawing comprises three folding screen sections, A, B, C, hinged together on'their meeting vertical edges by sets of double acting hinges I whereby the sections may be folded or adjusted to any angularity in the manner of an ordinary folding screen.

Each section A, B, C, preferably comprises a tall narrow rectangular frame of light soft wood such as white pine, said frames consisting of side members 2, top members 3, and bottom members 4, having their meeting ends joined together in any suitable manner. The bottom members 4 are preferably of greater width than the side and top members, and are provided with short legs 5 adapted to rest upon the flooor. In order to provide the baflie with sufficient area I preferably make the sections A, B, C of such size that the total area of the baffle when in normal use will be substantia1ly5 feet wide and 5 or 6 feet high, al though I do not limit my bafile to such size.

The opening through each panel frame is closed by a sheet of highly acoustic material 6, preferably so-called Acousti-Celotex, (a cane felt material obtainable on the market, the acoustic surface of which is processed with partial perforations to on its acoustic face whereby the sound absorbing coefficient is approximately three times that of ordinary paneling material). The perforated acoustic face of the material 6 forms the rear face of the section, whereby any sound reflected from a wall against which or adjacent which the bafiie may be placed will be thereby dissipated, preventing development of any objectionable resonance. Other highly acoustic paneling material, whether of mineral or fibre composition having one face adapted for decorative treatment and the other face having a high sound absorption coeiiicient might however be used. The front faces of the acoustic panels 6, being less sound absorbing than the rear faces, are capable of decorative treatment which may be either applied as liquid coatings or may be applied as decorative fabrics I, while the rear faces of the panels have a high sound absorption coefficient. The baffles may be of Italian, French, Chinese, Modern, or any other desired design to suit individual tastes or requirements.

In the center of the acoustic panel 6 middle section B is a large opening 8, and an ornamental grille 9 at the front of the panel is placed over this opening. Behind the opening an electrodynamic loud speaker i0 is disposed as shown in Fig. 2, which loud speaker is preferably of the electro-dynamic type but may be of any other type. The loud speaker 10 is mounted upon a readily detachable stand D, consisting of legs ll and a top I2 securely connected together, a brace [3 extending between the legs adjacent the bottom of the stand. Top l2 has reduced portions In at its ends, through which bolt holes are provided whereby the stand D may be removably bolted to the side frames 2 of the center section B, as by means of thumb bolts I4 which engage tapped plates l5 countersunk into the side frames 2, of the section, as illustrated in Fig. 4. Hence stand D not only serves as a mounting for the loud speaker l0 but as a brace for the section thereby eliminating undue vibration. The stand D for the loud speaker is readily detachable for easy handling and may be quickly attached or detached by manipulating thumb bolts l4.

By the above construction, the sound waves emitted from loud speaker ID are projected through opening 8 in the middle section B of the baiiie, which opening may be covered by an ornamental grille or scroll 9 of laminated wood backed by grille cloth 9a. The bafiie may be designed to harmonize with the furnishings of the finest interior, and hence constitutes an article of furniture standard in design for decorative purposes well as for utility.

The side sections A and C together with the center section B are of sufficient area to prevent dampening of the sound waves of the lower register, and have a high sound absorbing coefficient dissipating reflective sound.

My baffle is practically a flat surface, and there are no enclosures to set up reverberation which would destroy the quality of music or speech, and it is large enough to obtain sufficient baflie effect for the reproduction of the lowest notes with uniform effectiveness, and the back of the surface has such a high sound absorption coefficient that any sound reflected from the wall is dissipated. Being fiat there is no air chamber to cause reverberation, and no cabinet to vibrate or rumble. A panel constructed entirely of wood, or any ordinary cabinet, tends to vibrate excessively and destroy the quality of sound reproduced. My entire baflie is constructed in such manner and of such materials as to eliminate excessive vibration of the device itself; also my baflie is constructed of material, the back of which is so processed as to dissipate any sound waves reflected from the wall of a room, preventing reverberation or echo effect.

Furthermore, my baffle is not restricted to use in a corner of a room, or to use against the walls of a room, but can be used in any location at any point in a room, in an enclosure of glass, canvas, or the like, or in a structure without enclosing walls, or even out of doors, and is complete in itself. Aside from its artistic desirability, my baffie has great merit in that it satisfies all acoustic requirements without being esthetically unacceptable.

I claim:

l. A baffle for loud speakers and the like comprising a foldable frame of sufficient area when opened to reproduce the fundamental frequencies of sound waves of the lower register, the rear face of the frame having a high sound absorption coeificient; said frame having an opening therethrough; and an electrodynamic loud speaker registering within the opening.

2. A bafile for loud. speakers and the like comprising a foldable frame of sufficient area when opened to reproduce the fundamental frequencies of sound waves of the lower register, the rear face of the frame having a high sound absorption coeflicient; said frame having an opening therethrough; a support connected with the frame;

and an electrodynamic loud speaker mounted on said support having a diaphragm registering within the opening.

3. A baflie for loud speakers and the like comprising a foldable frame of area when opened suflicient to reproduce the fundamental frequencies of sound waves of the lower register, said frame having its front face adapted for decorative treatment and its rear face having a high sound absorption coefficient; said frame having an opening therethrough, a support connected with the frame adjacent the opening at the sound absorbing face, and an electrodynamic loud speaker mounted on said support and registering with the opening.

4. A baflie for loud speakers and the like comprising a foldable frame of area when opened suflicient to reproduce the fundamental frequencies of sound waves down to cycles, said frame having a high sound absorption coefficient; and having an opening therethrough; a stand connected with the frame below the opening at the sound absorbing side of the frame, said stand bracing said frame; and an electrodynamic loud speaker mounted on said stand having a diaphragm registering with the opening.

5. A bafile for loud speakers and the like comprising a plurality of connected relatively adjustable sections of area sufficient in heighth and width to reproduce the fundamental frequencies of sound waves of the lower register, said sections each having one face with a high sound absorption coefficient; the middle section having an opening therethrough; a stand mounted adjacent the opening; and an electrodynamic loud speaker mounted on said stand having a diaphragm registering with the opening.

6. A bafile for loud speakers and the like comprising a plurality of connected relatively adjustable sections of area sufficient in heighth and width to reproduce the fundamental frequencies of sound waves of the lower register, said sections each having one face with a high sound absorption coefilcient; the middle section having an opening therethrough, a stand connected with the middle section below the opening at the sound absorbing face of the section, said stand bracing said frame; and an electrodynamic loud speaker mounted on said stand having a diaphragm registering with theopening.

7. A baffle for loud speakers and the like comprising a plurality of connected relatively adjustable frames of area sufficient in overall heighth and width to reproduce the fundamental frequencies of sound waves down to 50 cycles, panels mounted in said frames each having one face with a high sound absorption coefficient; the panel in the middle frame having an opening therethrough; a stand connected with the frame below the opening at the sound absorbing face of the frame, said stand bracing said frame; and an electrodynamic loud speaker mounted on said stand having a diaphragm registering with the opening.

8. A baflle for loud speakers and the like comprising a plurality of relatively adjustable frames hinged together on their vertical edges, said baffie being of area sufilcient in heighth and width to reproduce the fundamental frequencies of sound waves down to 50 cycles, panels mounted in said frames each having one face adapted for decorative treatment and the other face having a high sound absorption coefficient; the panel in the middle frame having an opening therethrough, an ornamental covering penetrable by sound waves over said opening; a stand connected with the frame below the opening at the sound absorbing face of the frame, said stand bracing said frame; and an electrodynamic loud speaker mounted on said stand having a diaphragm registering with the opening.

ARTHUR M. PFALZER. 

